1. Field of the Invention
The present invention relates to a light emitting device using microcrystals, and a process for producing the same.
2. Description of the Related Art
A light emitting device using a semiconductor, such as GaAs, a GaAsP mixed crystal, a GaAlAs mixed crystal, GaP and the like, has conventionally been developed. The light emitting device comprises a substrate having laminated thereon an n-type semiconductor layer, a light emitting layer and a p-type semiconductor layer in this order, and when a voltage is applied in the normal bias direction, light emission occurs by recombination of an electron and a hole in the light emitting layer. Conventionally, the n-type semiconductor layer, the light emitting layer and the p-type semiconductor layer each are constituted with a single crystal, and are formed by epitaxial growth on the substrate. Therefore, the substrate is also constituted with a single crystal.
However, in the conventional light emitting device, because the n-type semiconductor layer, the light emitting layer and the p-type semiconductor layer each are constituted with a single crystal, lattice matching with the substrate and matching of the crystalline structures are necessary to obtain a good crystal. Furthermore, the conditions on conducting the epitaxial growth are severely restricted, and the epitaxial growth should be conducted at a high temperature to decrease defects. Accordingly, a material constituting the substrate is considerably restricted, and the freedom of selecting the materials is small. Therefore, quartz and glass cannot be used as the substrate, and there is a problem in that a device array of a large area cannot be produced.
Furthermore, the materials constituting the light emitting layer, the n-type semiconductor layer and the p-type semiconductor layer are considerably restricted by the material of the substrate, and the freedom of selecting the materials is small. Accordingly, there is also a problem in that the wavelength of emitting light is restricted. Furthermore, there is also a problem in that defects cannot be completely avoided even though such measures for reducing defects have been conducted, and the defects function as a non-light emission center to cause reduction or deterioration of the light emission efficiency.
The invention has been made in view of the problems, and an object thereof is to provide a light emitting device and a process for producing the same, that has a high light emission efficiency, a wide range of selection of the materials, and capability of forming a device array of a large area.
A light emitting device of the invention comprises a first conductive type layer, a second conductive type layer, and a microcrystalline layer comprising plural microcrystals comprising a semiconductor, formed between the first conductive type layer and the second conductive type layer.
Another light emitting device of the invention comprises a first conductive type clad layer, a second conductive type clad layer, a light emitting layer containing plural microcrystals, formed between the first conductive type clad layer and the second conductive type clad layer, and an insulating layer having a thickness thinner than the light emitting layer, formed between the first conductive type clad layer and the second conductive type clad layer.
A process for producing a light emitting device of the invention comprises a step of forming a first conductive type layer; a step of forming a microcrystalline layer containing plural microcrystals comprising a semiconductor on the first conductive type layer; and a step of forming a second conductive type layer on the first conductive type layer through the microcrystalline layer.
Another process for producing a light emitting device of the invention comprises a step of forming a first conductive type clad layer; a step of forming a light emitting layer comprising plural microcrystals, on the first conductive type clad layer; a step of forming an insulating layer having a thickness thinner than the light emitting layer, on the first conductive type clad layer; and a step of forming a second conductive type clad layer on the first conductive type clad layer through the light emitting layer and said insulating layer.
In the light emitting device according to the invention, when a voltage is applied between the first conductive type layer and the second conductive type layer, an electric current is injected to the microcrystals of the microcrystalline layer to occur emission of light. The microcrystals have substantially no defect, and emission of light occurs with a high efficiency.
In the another light emitting device according to the invention, when a voltage is applied between the first conductive type clad layer and the second conductive type clad layer, an electric current is injected to the microcrystals of the light emitting layer to occur emission of light. The microcrystals have substantially no defect, and emission of light occurs with a high efficiency. Because the insulating layer is formed between the first conductive type clad layer and the second conductive type clad layer, a leaking electric current between the first conductive type clad layer and the second conductive type clad layer is decreased, and the electric current flows via the respective microcrystals.
In the process for producing a light emitting device according to the invention, after the first conductive type layer is formed, the microcrystalline layer is formed, and the second conductive type layer is formed through the microcrystalline layer.
In the another process for producing a light emitting device according to the invention, after the first conductive type clad layer is formed, the microcrystalline layer is formed, and the insulating layer is formed. Thereafter, the second conductive type layer is formed through the microcrystalline layer and the insulating layer.